The dogs featured in the film would often have their tails tied down to their legs because the dogs would be enjoying themselves so much that they would wag their tails during filming. This tactic was missed once in the editing where they show Cujo from behind ready to attack and his tail is wagging energetically.
Star Dee Wallace said she has often been praised by parents for the scene where a hysterical Donna screams at Tad in a moment of frustrated terror. She said its a scene only a parent could identify with.
The original novel was a sequel of sorts following The Dead Zone. Since killer Frank Dodd was killed he became a kind of bogeyman in Castle Rock and supposedly haunted Tad. It is hinted that Dodd possessed Cujo. Sheriff George Bannerman, played by Sandy Ward here, makes specific references to Dead Zone hero Johnny Smith. Both this movie and The Dead Zone (1983) were developed at the same time, with this film released two months before, by different studios so the references were removed.
Young star Danny Pintauro was only six years old at the time of the movie and had not learned how to read yet. He would often have to memorize his lines from the script with the help of his mother who was always close by on location.
Stunt double Jean Coulter was in the car and had one of the toys used by the dogs' trainers as a "lure". The window was partially down, the dog jumped up and put his paws on the window, forcing it down and he reached in for his toy. Jeannie's reaction was to lower the toy and the dog bit her nose. She was treated at the hospital and released. There was also the rumor at the time that she was bitten by a rabid dog which was entirely incorrect.
The scenes where Donna and Tad are trapped by Cujo are suppose to be sweltering hot and appear that way on film. Yet the conditions were actually very cold during filming. At one point it got so cold inside the car that heaters were placed inside to keep the actors warm, but they would have to be turned off for shooting to prevent their sound from interfering.
Donna takes Tad into the house for his nap, after Vic fails to fix the car. The camera moves to a view of the woodlands and ocean in front of the house. The woodland area is the same location where The Howling was filmed, also starting Dee Wallace.
The character Sherrif Bannerman also appears in The Dead Zone (1983), played by Tom Skerritt. The original novel functions as an indirect sequel, as the serial killer Frank Dodd is mentioned several times, and may have possessed Cujo.
Shot in the same Mendocino, California community as the film Dead & Buried (1981). In fact in one shot the Pinto can be seen driving past the same church, with the 'reaper' shaped steeple, that's featured in Dead & Buried.
At one point the script for Cujo came to acclaimed horror director John Carpenter, however, Carpenter passed on directing as he didn't find the story particularly appealing. John Carpenter would later direct the Stephen King-based film Christine which came out the same year as Cujo.
The trivia items below may give away important plot points.
In the original Stephen King novel, Tad Trenton dies of dehydration while Donna contracts rabies from her fight with Cujo. There was a rabies scare following the incident, not mentioned in the film. The outcome of the Sharp account was not mentioned, in the book he had saved it.